1. Field
The present invention relates generally to wireless communications systems, and more specifically, to improvements in the operation of a medium access control (MAC) layer of an access terminal in a wireless communication system.
2. Background
Communication systems have been developed to allow transmission of information signals from an origination station to a physically distinct destination station. In transmitting information signal from the origination station over a communication channel, the information signal is first converted into a form suitable for efficient transmission over the communication channel. Conversion, or modulation, of the information signal involves varying a parameter of a carrier wave in accordance with the information signal in such a way that the spectrum of the resulting modulated carrier is confined within the communication channel bandwidth. At the destination station the original information signal is replicated from the modulated carrier wave received over the communication channel. Such a replication is generally achieved by using an inverse of the modulation process employed by the origination station.
Modulation also facilitates multiple-access, i.e., simultaneous transmission and/or reception, of several signals over a common communication channel. Multiple-access communication systems often include a plurality of remote subscriber units requiring intermittent service of relatively short duration rather than continuous access to the common communication channel. Several multiple-access techniques are known in the art, such as code division multiple-access (CDMA), time division multiple-access (TDMA), frequency division multiple-access (FDMA), and amplitude modulation multiple-access (AM).
A multiple-access communication system may be a wireless or wire-line and may carry voice and/or data. In a multiple-access communication system, communications between users are conducted through one or more base stations. A first user on one subscriber station communicates to a second user on a second subscriber station by transmitting data on a reverse link to a base station. The base station receives the data and may route the data to another base station. The data is transmitted on a forward channel of the same base station, or the other base station, to the second subscriber station. The forward channel refers to transmission from a base station to a subscriber station and the reverse channel refers to transmission from a subscriber station to a base station. Likewise, the communication may be conducted between a first user on one mobile subscriber station and a second user on a landline station. A base station receives the data from the user on a reverse channel, and routes the data through a public switched telephone network (PSTN) to the second user. In many communication systems, e.g., IS-95, W-CDMA, IS-2000, the forward channel and the reverse channel are allocated separate frequencies.
An example of a data optimized communication system is a high data rate (HDR) communication system. In an HDR communication system, the base station is sometimes referred to as an access network, and the remote station is sometimes referred to as an access terminal (AT). Functionality performed by an AT may be organized as a stack of layers, including a medium access control (MAC) layer. The MAC layer offers certain services to higher layers, including services that are related to the operation of the reverse channel. Benefits may be realized by improvements in the operation of a MAC layer of an AT in a wireless communication system.